Electrical switches are widely used in microwave and millimeter wave integrated circuits (MMICs) for many telecommunications applications, including signal routing devices, impedance matching networks, and adjustable gain amplifiers. State of the art technology generally relies on compound solid state switches, such as GaAs MESFETs and PIN diodes, for example. Conventional RF switches using transistors, however, typically provide low breakdown voltage (e.g., 30 V), relatively high on-resistance (e.g., 0.5 .OMEGA.), and relatively low off-resistance (e.g., 50 k.OMEGA. at 100 MHz). When the signal frequency exceeds about 1 GHz, solid state switches suffer from large insertion loss (typically on the order of 1 dB) in the "On" state (i.e., closed circuit) and poor electrical isolation (typically no better than -30 dB) in the "Off" state (i.e., open circuit).
Switches for telecommunications applications require a large dynamic range between on-state and off-state impedances in the RF regime. RF switches manufactured using micromachining techniques can have advantages over conventional transistors because they function more like macroscopic mechanical switches, but without the bulk and high cost. Micromachined, integrated RF switches are difficult to implement, however, because of the proximity of the contact electrodes to each other. Achieving a large off/on impedance ratio requires a good electrical contact with minimal resistance when the switch is on (closed circuit) and low parasitic capacitive coupling when the switch is off (open circuit). In the RF regime, close electrode proximity allows signals to be coupled between the contact electrodes when the switch is in the off-state, resulting in low off-state resistance. Lack of dynamic range in on to off impedances for frequencies above 1 GHz is the major limitation of conventional transistor-based switches and known miniature electromechanical switches and relays. Thus, there is a need in telecommunications systems for micro electromechanical switches that provide a wide dynamic impedance range from on to off at signal frequencies from DC up to at least 4 GHz.